Cruising Catamarans (ASA 114)

Prerequisites

ASA 101, 103 and 104, or equivalent experience skippering a monohull cruiser.
Points of sail, reefing a mainsail and basic anchoring.
Close-quarters handling of a single-engine boat.

Learning Objectives

ASA 114 Cruising Catamaran covers catamaran design, onboard systems, safety (including jacklines and the risk of capsize), sailing and powering in tight spaces, twin-engine handling, man-overboard recovery and heavy weather. Certification requires both on-water skills and a written exam. By the end of this lesson you will be able to:

Explain how a catamaran behaves differently from a monohull.
Turn and pivot a cat with differential thrust.
Decide when to reef using wind speed, since the boat does not heel.
Handle a squall on a catamaran.
Anchor with a bridle and pick up a mooring.

How a Catamaran Differs

A cruising catamaran has two narrow hulls joined by a bridgedeck. That gives it:

Form stability. Its stability comes from its wide beam, not from a heavy keel. It sails nearly flat.
No heeling warning. A monohull heels and rounds up when overpowered. A cat stays level, so the load goes into the rig, sails and hulls instead.
High windage. The tall cabin and two hulls catch a lot of wind. A cat can drift fast with no sails up and gets blown sideways easily in close quarters.
Little carry. With no deep keel, a cat coasts poorly and stops quickly once you take the power off.
Two engines, far apart. One in each hull, which lets you turn the boat almost in its own length.

A catamaran also cannot right itself once capsized. Capsize is rare in cruising cats, but avoiding it depends on the skipper reducing sail early.

Twin-Engine Handling: Differential Thrust

With an engine in each hull, you steer at low speed mainly with the throttles, not the rudders.

Pivoting in Place

Put one engine in forward and the other in reverse with similar power. The boat spins around its centre without moving ahead or astern.

To turn to port: starboard engine ahead, port engine astern.
To turn to starboard: port engine ahead, starboard engine astern.

A useful rule: the bow turns away from the engine going ahead. The starboard engine pushing ahead pushes the starboard hull forward, swinging the bow to port.

At first, keep the rudders centred. They do little at low speed and add another variable while you learn. Because turning does not depend on water flowing over the rudders, a cat can be manoeuvred at very low speed. Go slowly: small throttle movements, and give the boat time to respond.

Fine-tune the pivot by changing the balance. Slightly more forward than reverse makes the boat creep ahead while turning, and slightly more reverse makes it creep back.

Wind and Current from the Side

With wind on the beam, the bows tend to blow off. Use more forward thrust on the windward engine to hold the bows up, and just enough on the leeward engine to keep the boat moving. Practise in open water first, then in a breeze, to learn how much your boat's windage pushes it.

Prop Walk

On a single-engine boat, prop walk pulls the stern sideways in reverse. On most cats the propellers turn in opposite directions, so their side-forces largely cancel when both engines are in the same gear. Reversing in a straight line is much easier than on a monohull.

Sail Trim and Reefing by Wind Speed

Because a cat does not heel, you cannot use heel to tell you when to reef. Use wind speed and the boat's behaviour instead. An overpowered cat accelerates, digs in its leeward bow and loads its rig until something breaks.

When to Reef

Your boat's manual is the first reference. As a starting point, one catamaran school suggests reefing by apparent wind:

First reef at about 18–20 knots.
Second reef at about 25 knots.
Third reef at a steady 28–30 knots.
Above 30 knots and gusting, furl the jib and sail on the deep-reefed main.

These are guides only. Every design differs. Other sources recommend reefing on true wind, since apparent wind drops when you bear away and rises again when you turn upwind. Either way, the old rule holds: reef early, before it becomes hard to do.

Also watch the leeward hull. If it is pressed deep and the bow is burying, you have too much sail up.

Downwind

Cats speed up downwind, which lowers the apparent wind and can hide how much true wind is blowing. Before turning upwind, check the true wind speed. A common reminder for gusts is "steer down in a puff" to bear away and take load off the rig.

Reefing Technique

Practise at the dock until you can tie a reef in under three minutes. A typical order:

Ease the mainsheet (drop the traveller to leeward).
Take up the topping lift.
Ease the halyard to a pre-marked point.
Pull in and secure the reef line.
Re-tension the halyard.
Trim the sheet.

Many cats sail well on the jib alone but poorly on the main alone. If you need to reduce sail quickly, roll out or keep the jib and drop the main.

Squalls

When a squall comes:

Roll away the jib so it does not flog itself to pieces.
Turn onto a beam reach.
Ease the mainsheet to spill wind, letting the fully battened main luff.
Hold a beam reach until the squall passes. In severe squalls, start the engines to keep control.

Anchoring with a Bridle

Without a bridle, a cat tends to sail around its anchor and swing from side to side. A bridle is a Y of line from each bow, joined at a chain hook in the middle.

Lower the anchor and pay out chain as the boat drifts back.
Clip the bridle's hook onto a link of the chain, with the hook fully closed.
Let out more chain so the bridle takes the load and the chain hangs in a loop under the bridgedeck. The bridle spreads the load between both hulls and holds the bows into the wind.
Scope as a multiple of depth: about 3–4 times in light winds, 5–7 times above about 20 knots.
Set the anchor by backing on both engines, then check transits on land to confirm it is not dragging.

To weigh anchor, run the engines, pull in chain until the bridle comes to the bow, unhook it, then lift the rest of the chain while edging gently forward.

Picking Up a Mooring

Rig the bridle (or one line from each hull) before you approach. Come in slowly, from as far downwind or down-current as possible. A crew member on the forward crossbeam with a long boathook picks up the pennant. The helm cannot see the buoy under the bows at the last moment, so agree hand signals in advance. Be ready to stop quickly with a burst of reverse.

Worked Example: Leaving a Crowded Anchorage

You are anchored on a bridle in a crowded bay, with 15 knots of wind on the nose and boats close astern.

Start both engines and brief the crew.
Motor gently up the chain while the windlass brings it in. Unclip the bridle when it reaches the bow.
Once the anchor breaks out, the bows start to fall off to starboard. Push the port engine ahead and the starboard engine astern to pivot the bows back into the wind.
With the anchor up, use differential thrust to turn in your own length and motor out between the boats.

Common Mistakes

Waiting for heel or weather helm before reefing. A catamaran will not give that warning.
Using too much throttle in close quarters. Small inputs and patience work better.
Forgetting windage and getting blown down onto other boats when manoeuvring slowly.
Anchoring without a bridle, so the boat sails around the anchor.
Expecting the boat to coast into a berth. A cat stops quickly once the power is off.

Summary

A catamaran sails flat, has high windage and stops quickly.
Pivot with one engine ahead and one astern. The bow turns away from the engine going ahead.
Reef by wind speed, not heel: as a guide, around 18–20, 25 and 28–30 knots apparent. Reef early.
In a squall, furl the jib, bear onto a beam reach and luff the main.
Anchor with a bridle to hold the bows into the wind and spread the load.

Check Your Understanding

You want to spin a cat to starboard. Which engine goes ahead? The port engine ahead, with the starboard engine astern.
Why can't you use heel to decide when to reef a catamaran? It sails almost flat, so overpowering shows up as speed and load on the rig instead of heel.
What is a starting-point apparent wind speed for the first reef? About 18–20 knots, checked against the boat's manual.
What does an anchor bridle do? It holds the bows into the wind, stops the cat sailing around its anchor and spreads the load between the hulls.
In a squall, which sail do you furl first? The jib, so it does not flog.

Sources

https://americansailing.com/certifications/asa-114-cruising-catamaran/
https://www.cruisingworld.com/controlling-your-sails-on-catamaran/
https://www.cruisingworld.com/how/how-dock-and-swing-catamaran/
https://catamaranguru.com/when-to-reef-the-sails-on-a-catamaran/
https://www.themultihullgroup.com/inspire-and-learn-how-to-anchor-and-set-up-bridle/
https://blog.marineverse.com/nauticed/marineverse/2025/12/19/catamaran-docking-marineverse.html